I'm trying to figure out just what happened to our 87 F250. Worker brought it to our shop running very rough, saying no power. This is a rebuilt engine w/3742 mi on it. It also has a Stealth intake, Edelbrock 750 carb, Howards single pattern cam 213@.050, .501 lift, 108 centerline, some ex port work and a MSD HEI style distributor. So far-

Has a slight pop in the intake when starting, takes alot of pumping on the accelorator to start, good fuel spray in carb barrells when doing this.
Vac @ 15 and fluttering, motor shaking
New autolite copper plugs and wells premium wires, new cap/rotor/module, spark is real good, timing@ 10 BTDC
Fuel psi is a rock steady 6.5 psi @ carb inlet, carb works perfect
Compression is 184 highest to 179 lowest
Pulled the valve covers and all pushrods/rockers appear to be moving properly, but we did not measure lift.
And the most alarming- when you rev it past 4000 rpm the oil psi drops to nothing untill below 4000 when it comes back to 40psi(idle) and is at 65psi and is rock steady untill it drops. It shows this in the factory guage as well as the snap on test guage. Oil is clean has 6qts in the pan and reads full on the stick also.
What have we missed here?

 

The pop sounds like a possible sticky intake valve? which would also give the rough running, and vacuum flutter.

Adjustable rockers? Time to check lash. Might have a tight one.

What oil pump? stock? HV?? If a HV, you could be sucking the pan dry at 4000 rpm, thus making it lose oil pressure. OR..........how well was the oil pickup tube height set?? If it was not checked, it could be too high off the bottom of the pan and once you suck enough oil out at high rpm, it drops below the pickup tube=no oil pressure. Could put another quart of oil in and try again. That might narrow it down, maybe. Won't fix it, per say.

Just some thoughts I had.

 

Rebuilt (by local shop) 460 from rolled 87 E-350 we bought at auction for $350. Riveted plate on block said the date/milage it was done at and it had 4 months of use and 1943 mi. It was a very stock type rebuild so I wil assume a stock replacement oi pump.
As the van oil pan was different than our truck we changed the pan and pickup and used some play dough to set the pickup about 1/2" off the pan floor. Will try the extra qt thing when we get the other headache solved.
The rocker system is the stock net lash system, they had shims under the pedistals and when we changed the cam those shims were removed so we could restore a little preload to the lifters, as we had basically had no preload at the lifters with the shims.
We used sealed power lifters on the Howards cam we put in, also a summit racing double roller timing chain to spin it. It coud be sticking valves but what realy bothers me is that we put this truck back in service in May of this yr and it had none of these problems untill now.

 

Couldn't it still be the carb or ignition system. Carb - just pumping gas doesn't mean floats aren't stuck, jets clogged or choke acting up. Ign - cap rotor, wires, plugs check in the dark - sparks flying?

 

Could be timing issue, misfiring a cylinder with the intake vavle open?

The shak'n at idle could still be a misfiring cylinder(plug wires/cap)or valve issue. That HEI style distributor could be a problem? Maybe a new cap would be a start?

 

Just replaced all the plugs/cap/rotor/ign module/wires and there are no sparks in a dark area. Carb seams to be working perfectly- We took it off and put it on a 396 chevy engine we have and it works just fine......